BRUSSELS (AP) — Two years after winding down its military operation in Afghanistan, NATO has agreed to send more troops to the war-ravaged country to help train and work alongside the Afghan security forces.

The move comes in response to a request from NATO commanders to provide around 3,000 troops.

Speaking ahead of NATO defense ministers' meeting in Brussels Thursday, Secretary-General Jens Stoltenberg said that "15 nations have already pledged additional contributions" and that he expected more pledges later in the day.

Britain has said that it would contribute just under 100 troops in a non-combat role.

"We're in it for the long haul. It's a democracy. It's asked for our help and it's important that Europe responds," British Defense Secretary Michael Fallon told reporters. "Transnational terror groups operate in Afghanistan, are a threat to us in Western Europe."

European allies and Canada are waiting to hear what U.S. Defense Secretary Jim Mattis will offer, or indeed seek from them.

Stoltenberg said the increase does not mean the alliance will once again combat the Taliban and extremist groups there.

However he conceded "there are many problems, and many challenges and many difficulties, and still uncertainty and violence in Afghanistan.

"What we do is not to conduct combat operations but to help the Afghans fight, and to help the Afghans take full responsibility for the security in their own country," he said.

NATO particularly wants to train more Afghan special operations forces, which are key to countering Taliban insurgents and extremist groups undermining the weak central government in Kabul. The alliance also wants to help build up the country's fledgling air force and train pilots. Another aim is to improve officer leadership standards.